Clusters of life-threatening ventricular arrhythmias in patients with implanted cardioverter-defibrillators: Prevalence, characteristics, and risk stratification

Background: Series of discharges from an implanted defibrillator (ICD) to t erminate life-threatening ventricular tachyarrhythmias are one particular a spect of energy nse and success of ICD therapy. Little is known about preva lence, characteristics, and risk stratification of so-called "cluster arrhy thmias." Hypothesis: The objective of this study was to examine the frequency of clu ster arrhythmias, to characterize the temporal relationship precisely, and to assess the accompanying circumstances of their occurrence, whereby risk stratification was to be made if appropriate. Methods: In all, 63 consecutive patients were followed prospectively over 7 27 +/- 684 days to determine the presence and characteristics of cluster ar rhythmias (45,801 patient days). In 30 patients, 374 ICD episodes of ventri cular tachyarrhythmias were analyzed for their temporal relationship. After a first successfully terminated ventricular tachyarrhythmia. further ICD d ischarges within 3 h were observed during 145 of 374 (39%) episodes; mean t ime interval between these arrhythmias was 25 +/- 32 min. Results: Arrhythmia clusters occurred in 19 of 30 (63%) patients. In multiv ariate analysis, only underlying heart disease was predictive for accumulat ion of ventricular tachyarrhythmias. Cluster arrhythmias were more frequent among patients with ischemic heart disease than among those with nonischem ic heart disease (40.0 vs. 29.2%, p<0.05). Ejection fraction, age, gender, and other parameters were not predictive for occurrence of arrhythmia clust ers. In 4 of 19 patients, accumulation of ICD discharges was predictive for new onset of myocardial ischemia elicited by exercise test. Conclusions: Cluster arrhythmias are most common in patients with ICDs with coronary heart disease and may indicate disease progression and increasing instability, for example, due to new onset of myocardial ischemia.